Exhaust heat recovery system, energy supply system, and exhaust heat recovery method

ABSTRACT

The object of the present invention is to enhance available energy recovery efficiency compared to an exhaust heat recovery method by generation of water vapor. In order to achieve this object, the present invention adopts a configuration including a thermal conduction path ( 1 ) which conducts exhaust heat, and a high-boiling-point heat medium vapor generator ( 2 ) which generates high-boiling-point heat medium vapor (R 2 ) by heat exchange between the exhaust heat which is conducted through the thermal conduction path ( 1 ) and a high-boiling-point heat medium (R 1 ) that has a higher evaporation temperature than water (R 3 ).

TECHNICAL FIELD

The present invention relates to an exhaust heat recovery system, an energy supply system, and an exhaust heat recovery method.

Priority is claimed on Japanese Patent Application No. 2010-034776, filed Feb. 19, 2010, the content of which is incorporated herein by reference.

BACKGROUND ART

As is well known, with respect to a variety of systems including cogeneration systems, power generation systems such as thermal power plants, as well as steam generation equipment such as boilers, the energy efficiency of equipment is enhanced by recovering the heat of combustion exhaust gas (exhaust heat recovery). The below-mentioned Patent Document 1 discloses an example of cogeneration equipment (cogeneration system) using exhaust heat recovery boilers; the below-mentioned Patent Document 2 discloses an example of a vertical natural-circulation exhaust-heat-recovery boiler of the multi-pressure type; the below-mentioned Patent Document 3 discloses an example of a combined cycle power plant which combines exhaust heat recovery boilers; and the below-mentioned Patent Document 4 discloses an example of a multi-pressure type exhaust heat recovery boiler.

Cogeneration systems are known as energy supply systems which extract thermal energy used in heating/cooling, hot-water supply and the like by utilizing the exhaust heat produced during power generation. In such cogeneration systems, exhaust heat recovery is commonly performed by generating water vapor using exhaust-heat-recovery boilers, as described in Patent Document 1.

In addition, Patent Document 5 discloses a waste-heat-recovery apparatus which recovers waste heat (exhaust heat) from a comparatively low-temperature heat source on the order of 200° C. using first and second working fluids with different boiling points. This waste-heat recovery apparatus uses water as the first working fluid, and freon or a freon substitute with a lower boiling point than water, more specifically, chlorofluorocarbon, hydrochlorofluorocarbon, hydrofluorocarbon, ammonia, ammonia water or the like, as the second working fluid, thereby enhancing power generation efficiency by recovering larger amounts of heat from a comparatively low-temperature heat source.

CITATION LIST Patent Document

-   Patent Document 1: Japanese Unexamined Patent Application, First     Publication No. 2003-021302 -   Patent Document 2: Japanese Unexamined Patent Application, First     Publication No. 2000-346303 -   Patent Document 3: Japanese Unexamined Patent Application, First     Publication No. 2002-021583 -   Patent Document 4: Japanese Patent Publication No. 2753169 -   Patent Document 5: Japanese Unexamined Patent Application, First     Publication No. 2008-267341

SUMMARY OF INVENTION Technical Problem

However, with respect to the aforementioned conventional exhaust heat recovery method by generation of water vapor from water, the recovery efficiency of available energy capable of being recovered from the energy possessed by exhaust gas (exhaust heat) is not necessarily sufficient, and further improvements in available energy recovery efficiency are anticipated. In particular, with respect to exhaust heat recovery of high-temperature exhaust heat that far exceeds water evaporation temperature such as exhaust heat of comparatively high-temperature exceeding, for example, 300° C., there are limits on evaporation temperature during water vaporization. Consequently, the current situation is that the available energy recovery efficiency of conventional exhaust heat recovery methods is insufficient, necessitating the loss of large amounts of available energy. The aforementioned available energy is a thermodynamic concept that is also called “exergy,” and is commonly known as energy which is extracted from a system as mechanical work. Available energy in the invention of the present patent application signifies energy (an amount of work) that can be recovered as mechanical work (dynamic force of electricity or the like) from among the total energy possessed by exhaust gas.

Moreover, the conventional exhaust heat recovery method which uses water (a first working fluid) and a second working fluid with a lower boiling point than the water is intended for heat recovery from a comparatively low-temperature heat source on the order of 200° C. As the temperature of vapor obtained by vaporization of the second working fluid is still lower than the temperature of vapor obtained by vaporization of the first working fluid, recovery of available energy from exhaust heat of comparatively high temperature is almost impossible.

The object of the present invention is to improve available energy recovery efficiency beyond that of an exhaust heat recovery method which obtains available energy by vaporization of water, and an exhaust heat recovery method which obtains available energy by vaporization of water and a fluid with a lower boiling point than the water.

Another object of the present invention is to offer an energy supply system with a higher efficiency, energy-saving rate, and CO₂ reduction rate than the prior art.

Solution to Problem

In order to achieve the foregoing objectives, as a means of solution pertaining to an exhaust heat recovery system, the present invention provides a thermal conduction path which conducts exhaust heat, and a high-boiling-point heat medium vapor generator which generates high-boiling-point heat medium vapor by heat exchange between a high-boiling-point heat medium that has a higher evaporation temperature than water and the exhaust heat conducted through the thermal conduction path.

Advantageous Effects of Invention

According to the present invention, instead of generating water vapor by vaporization of water, or in addition to generating water vapor by vaporization of water, high-boiling-point heat medium vapor is generated by causing evaporation of a high-boiling-point heat medium that has a higher evaporation temperature than water (i.e., a lower vapor pressure than water), with the result that it is possible to improve available energy recovery efficiency beyond that of conventional exhaust heat recovery methods which generate water vapor by evaporating water.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a system block diagram which shows the functional configuration of an energy supply system P1 of a first embodiment of the present invention.

FIG. 2 is a characteristic diagram which shows the heat exchange conditions of each heat medium of an exhaust heat recovery unit K1 of the energy supply system P1 of the first embodiment of the present invention in relation to exchanged heat amount (horizontal axis) and temperature (vertical axis).

FIG. 3 is a system block diagram which shows the functional configuration of an energy supply system P2 of a second embodiment of the present invention.

FIG. 4 is a characteristic diagram which shows the heat exchange conditions of each heat medium of an exhaust heat recovery unit K2 of the energy supply system P2 of the second embodiment of the present invention in relation to exchanged heat amount (horizontal axis) and temperature (vertical axis).

FIG. 5 is a characteristic diagram which shows energy-saving rates when ethylene glycol and diethylene glycol are adopted as a high-boiling-point heat medium R1 in the second embodiment of the present invention.

FIG. 6 is a characteristic diagram which shows CO₂ reduction rates when ethylene glycol and diethylene glycol are adopted as the high-boiling-point heat medium R1 in the second embodiment of the present invention.

FIG. 7 is a system block diagram which shows the functional configuration of an energy supply system P3 of a third embodiment of the present invention.

FIG. 8 is a characteristic diagram which shows the heat exchange conditions of each heat medium of an exhaust heat recovery unit K3 of the energy supply system P3 of the third embodiment of the present invention in relation to exchanged heat amount (horizontal axis) and temperature (vertical axis).

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention are described below with reference to drawings.

First Embodiment

First, a first embodiment of the present invention is described with reference to FIGS. 1 and 2.

As shown in FIG. 1, an energy supply system P1 of the first embodiment includes an exhaust gas pipe 1, a high-boiling-point heat medium vapor generator 2, a water vapor generator 3, a high-boiling-point heat medium preheater 4, a water preheater 5, a high-boiling-point heat medium vapor superheater 6, a water vapor superheater 7, a high-boiling-point heat medium supply pump 8, a water supply pump 9, a high-boiling-point heat medium vapor turbine power generator 10, a high-boiling-point heat medium vapor condenser 11, a liquid collection tank 12, a water vapor turbine power generator 13, a water vapor condenser 14, a water collection tank 15, and a cooling water supply device 16. In FIG. 1, the reference symbol G indicates high-temperature exhaust gas, R1 indicates a high-boiling-point heat medium, R2 indicates high-boiling-point heat medium vapor, R3 indicates water, and R4 indicates water vapor.

Among these respective components, the exhaust gas pipe 1, the high-boiling-point heat medium vapor generator 2, the water vapor generator 3, the high-boiling-point heat medium preheater 4, the water preheater 5, the high-boiling-point heat medium vapor superheater 6, and the water vapor superheater 7 constitute an exhaust heat recovery unit K1 which recovers exhaust heat from the high-temperature exhaust gas G. The exhaust heat recovery unit K1 corresponds to an exhaust heat recovery system of the present invention.

Among the foregoing components, the high-boiling-point heat medium supply pump 8, the water supply pump 9, the high-boiling-point heat medium vapor turbine power generator 10, the high-boiling-point heat medium vapor condenser 11, the liquid collection tank 12, the water vapor turbine power generator 13, the water vapor condenser 14, the water collection tank 15, and the cooling water supply device 16 constitute a power generation unit W. The power generation unit W is a dynamic force generator which generates power (dynamic force) using the high-boiling-point heat medium R2 and the water vapor R4 as working fluids by supplying, to the exhaust heat recovery unit K1, the high-boiling-point heat medium R1 and the water R3 which are the liquid heat mediums, and recovering, from the exhaust heat recovery unit K1, the high-boiling-point heat medium vapor R2 and the water vapor R4 obtained by vaporizing these liquid mediums by the aforementioned exhaust heat. The energy supply system P1 is composed from the exhaust heat recovery unit K1 and the power generation unit W (dynamic force generator), and is a power generation system which generates power that is one mode of dynamic force by the high-boiling-point heat medium vapor R2 and the water vapor R4 generated by recovering exhaust heat from the high-temperature exhaust gas G in the exhaust heat recovery unit K1.

In this type of energy supply system P1, the exhaust gas pipe 1 is a thermal conduction path through which flows the high-temperature exhaust gas G that is supplied from the exterior. The high-temperature exhaust gas G is exhaust gas of high temperature (i.e., gas charged with exhaust heat) that is discharged, for example, from a combustor, and has a temperature, for example, a temperature of 300° C. or more, far exceeding the temperature required for vaporizing the water R3. The high-temperature exhaust gas G circulates from the left side (upstream side) to the right side (downstream side) of the exhaust gas pipe 1, as shown in FIG. 1.

The high-boiling-point heat medium vapor generator 2 is provided at an intermediate location of the exhaust gas pipe 1, as shown in FIG. 1, and is a device which generates the high-boiling-point heat medium vapor R2 of high pressure by heat exchange between the high-boiling-point heat medium R1 and the high-temperature exhaust gas G. The water vapor generator 3 is provided on the downstream side of the high-boiling-point heat medium vapor generator 2 in the exhaust gas pipe 1, as shown in FIG. 1, and is a device (boiler) which generates the water vapor R4 of high pressure by heat exchange between the water R3 and the high-temperature exhaust gas G.

Here, the high-boiling-point heat medium R1 is a liquid which has a higher evaporation temperature than the water R3 (i.e., it has a lower evaporation pressure than the water R3) and which is a chemically stable compound in heat exchange with the high-temperature exhaust gas G. For example, one may cite ethylene glycol (molecular formula: C₂H₆O₂), diethylene glycol (molecular formula: C₂H₁₀O₃), propylene glycol (C₃H₈O₂), triethylene glycol (molecular formula: C₆H₁₄O₄), propylene carbonate (molecular formula: C₄H_(S)O₃), propylene ethylene glycol (molecular formula: C₃H₈O₂), formamide (molecular formula: CH₃NO), and so on.

As shown in FIG. 1, the high-boiling-point heat medium preheater 4 is provided between the high-boiling-point heat medium vapor generator 2 and the water vapor generator 3 in the exhaust gas pipe 1. The high-boiling-point heat medium preheater 4 is a type of heat exchanger which performs preheating the high-boiling-point heat medium R1 to, for example, a temperature just below boiling by heat exchange between the high-temperature exhaust gas G and the high-boiling-point heat medium R1 supplied from the high-boiling-point heat medium supply pump 8, and discharges the preheated high-boiling-point heat medium R1 to the high-boiling-point heat medium vapor generator 2.

As shown in FIG. 1, the water preheater 5 is provided on the downstream side of the water vapor generator 3 in the exhaust gas pipe 1. The water preheater 5 is a type of heat exchanger which performs preheating the water R3 to, for example, a temperature just below boiling by heat exchange between the high-temperature exhaust gas G and the water R3 supplied from the water supply pump 9, and discharges the preheated water R3 to the water vapor generator 3 and the high-boiling-point heat medium vapor condenser 11.

As shown in FIG. 1, the high-boiling-point heat medium vapor superheater 6 is provided on the upstream side of the high-boiling-point heat medium vapor generator 2 in the exhaust gas pipe 1. The high-boiling-point heat medium vapor superheater 6 is a type of heat exchanger which superheats the high-boiling-point heat medium vapor R2 supplied from the high-boiling-point heat medium vapor generator 2 by heat exchange with the high-temperature exhaust gas G, and discharges the superheated high-boiling-point heat medium vapor R2 to the high-boiling-point heat medium vapor turbine power generator 10.

As shown in FIG. 1, the water vapor superheater 7 is provided on the upstream side of the high-boiling-point heat medium vapor superheater 6 in the exhaust gas pipe 1. The water vapor superheater 7 is a type of heat exchanger which superheats the water vapor R4 supplied from the water vapor generator 3 and the high-boiling-point heat medium vapor condenser 11 by heat exchange with the high-temperature exhaust gas 0, and discharges the superheated water vapor R4 to the water vapor turbine power generator 13.

The high-boiling-point heat medium supply pump 8 is a pump which pumps out the high-boiling-point heat medium R1 from the liquid collection tank 12, and supplies it to the high-boiling-point heat medium preheater 4. The water supply pump 9 pumps out the water R3 from the water collection tank 15, and supplies it to the water preheater 5. The high-boiling-point heat medium vapor turbine power generator 10 is a turbine power generator which generates power by driving a power generator that is axially coupled to a turbine by rotating the turbine using the high-boiling-point heat medium vapor R2 of high pressure supplied from the high-boiling-point heat medium vapor generator 2 via the high-boiling-point heat medium vapor superheater 6.

The high-boiling-point heat medium vapor condenser 11 is a type of heat exchanger which condenses (liquefies) the high-boiling-point heat medium vapor R2 to restore it to the high-boiling-point heat medium R1, and which vaporizes the water R3 to produce the water vapor R4 of high pressure, and it does so by heat exchange between the high-boiling-point heat medium vapor R2 that is discharged from the turbine of the high-boiling-point heat medium vapor turbine power generator 10 after power recovery and the water R3 that is supplied from the water preheater 5. The high-boiling-point heat medium vapor condenser 11 discharges the restored high-boiling-point heat medium R1 to the liquid collection tank 12, and discharges the water vapor R4 produced by heat exchange with the high-boiling-point heat medium vapor R2 to the water vapor superheater 7.

The liquid collection tank 12 is a storage tank which temporarily stores the high-boiling-point heat medium R1 supplied from the high-boiling-point heat medium vapor condenser 11. The water vapor turbine power generator 13 is a turbine power generator which generates power by driving a power generator that is axially coupled to a turbine by rotating the turbine using the water vapor R4 of high pressure supplied from the water vapor generator 3 and the high-boiling-point heat medium vapor condenser 11 via the water vapor superheater 7.

The water vapor condenser 14 is a type of heat exchanger which condenses (liquefies) the water vapor R4 that is discharged from the turbine of the water vapor turbine power generator 13 after power recovery, and restores it to the water R3 by heat exchange with cooling water that is supplied from the cooling water supply device 16. The water vapor condenser 14 discharges the restored water R3 to the water collection tank 15. The water collection tank 15 is a storage tank which temporarily stores the water R3 supplied from the water vapor condenser 14. The cooling water supply device 16 is a device which performs circulating supply of the cooling water to the water vapor condenser 14.

Next, the operations of the energy supply system P1 of the first embodiment are described in detail with reference also to the characteristic diagram of FIG. 2.

In the energy supply system P1, multiple heat exchangers which carry out heat exchange with the high-temperature exhaust gas G are arranged in the direction from the upstream side to the downstream side of the exhaust gas pipe 1, i.e., in the axial direction of the exhaust gas pipe 1, as shown in FIG. 1. Specifically, among the various heat exchangers, the water vapor superheater 7 is positioned at the farthest upstream point of the exhaust gas pipe 1, and the high-boiling-point heat medium vapor superheater 6, the high-boiling-point heat medium vapor generator 2, the high-boiling-point heat medium preheater 4, the water vapor generator 3, and the water preheater 5 are disposed in this order toward the downstream side. Accordingly, since the high-temperature exhaust gas G which flows through the region (heat exchange region) of the exhaust gas pipe 1 where these heat exchangers are disposed is deprived of calorific value by each heat exchanger by transiting the heat exchange region from the upstream side to the downstream side, the temperature of the high-temperature exhaust gas G is higher toward the upstream side of the heat exchange region (i.e., the temperature of the high-temperature exhaust gas G is lower toward the downstream side).

Focusing on the high-boiling-point heat medium vapor generator 2 and the water vapor generator 3, since the high-boiling-point heat medium vapor generator 2 is located further toward the upstream side of the heat exchange region than the water vapor generator 3, the high-boiling-point heat medium R1 in the high-boiling-point heat medium vapor generator 2 carries out heat exchange with the high-temperature exhaust gas G of higher temperature than the water R3 in the water vapor generator 3.

FIG. 2 is a characteristic diagram which shows the heat exchange conditions of the respective heat mediums (i.e., the high-temperature exhaust gas G, the high-boiling-point heat medium R1, the high-boiling-point heat medium vapor R2, the water R3, and the water vapor R4) in the aforementioned heat exchange region in relation to exchanged heat amount (horizontal axis) and temperature (vertical axis). In FIG. 2, a line Lg shown by a solid line indicates the change in condition of the high-temperature exhaust gas G, a broken line Ls shown by a dotted line indicates the change in condition of the water R3 or the water vapor R4, and a broken line Lk shown by a dashed line indicates the change in condition of the high-boiling-point heat medium R1 or the high-boiling-point heat medium vapor R2.

As shown in FIG. 2, since the high-temperature exhaust gas G is deprived of calorific value by each heat exchanger, the relationship of the high-temperature exhaust gas G between the exchanged heat amount and the temperature is an approximately proportional relationship as shown by the line Lg. That is, in this characteristic diagram, an exchanged heat amount point A1 corresponds to the farthest downstream point of the heat exchange region, and an exchanged heat amount point C3 corresponds to the farthest upstream point of the heat exchange region. In terms of heat exchange properties, the respective heat exchangers are positioned between the exchanged heat amount point A1 (farthest downstream point) and the exchanged heat amount point C3 (farthest upstream point), and carry out heat exchange using the high-temperature exhaust gas G as the heat source.

When considering heat exchange of the water R3 and the water vapor R4 with the high-temperature exhaust gas G, i.e., heat exchange in the water preheater 5, the water vapor generator 3, and the water vapor superheater 7, the water R3 after preheating by the water preheater 5 is distributed and supplied to the water vapor generator 3 and the high-boiling-point heat medium vapor condenser 11. Some of the water R3 becomes the water vapor R4 as a result of heat exchange with the high-temperature exhaust gas G in the water vapor generator 3, and the remaining water R3 becomes the water vapor R4 as a result of heat exchange with the high-boiling-point heat medium vapor R2 in the high-boiling-point heat medium vapor condenser 11.

The region of the exchanged heat amount points A1 to A2 in the broken line Ls corresponds to the temperature rise (pressure increase) caused by the water preheater 5 until a temperature just below the boiling point of the water R3, and the region of the exchanged heat amount points A2 to B1 in the broken line Ls corresponds to vaporization of a portion of the water R3 (i.e., production of the water vapor R4) by the water vapor generator 3. Moreover, the region of the exchanged heat amount points B1 to D in the broken line Ls corresponds to vaporization of the remaining water R3 (i.e., production of the water vapor R4) by the high-boiling-point heat medium vapor condenser 11. That is, the water R3 which is preheated by the water preheater 5 to a temperature only slightly below the boiling point becomes the water vapor R4 by the exchanged heat amounts across the exchanged heat amount points A2 to D.

The water vapor R4 discharged from the water vapor generator 3 and the water vapor R4 discharged from the high-boiling-point heat medium vapor condenser 11 are merged, and supplied to the water vapor superheater 7. That is, the water vapor R4 generated by the water vapor generator 3 and the high-boiling-point heat medium vapor condenser 11 becomes the water vapor R4 (superheated water vapor) superheated beyond the boiling point by heat exchange with the high-temperature exhaust gas G in the water vapor superheater 7. The region of the exchanged heat amount points C2 to C3 in the broken line Ls is the superheated region of the water vapor R4 due to the water vapor superheater 7. The temperature of the exchanged heat amount point C2 corresponding to the superheating starting point of the water vapor R4 is equal to the temperature of the exchanged heat amount point D (vaporization termination point) of the water vapor R4 as illustrated in the drawing.

On the other hand, when considering heat exchange of the high-boiling-point heat medium R1 and the high-boiling-point heat medium vapor R2 with the high-temperature exhaust gas G, i.e., heat exchange in the high-boiling-point heat medium preheater 4, the high-boiling-point heat medium vapor generator 2, and the high-boiling-point heat medium vapor superheater 6, the high-boiling-point heat medium R1 is preheated to a temperature only slightly below boiling point by heat exchange with the high-temperature exhaust gas G in the high-boiling-point heat medium preheater 4, and is subsequently supplied to the high-boiling-point heat medium vapor generator 2 to become the high-boiling-point heat medium vapor R2. The region of the exchanged heat amount points B1 to B2 in the broken line Lk corresponds to the temperature rise (pressure increase) caused by the high-boiling-point heat medium preheater 4 to a temperature just below the boiling point of the high-boiling-point heat medium R1, and the region of the exchanged heat amount points B2 to C1 in the broken line Lk corresponds to vaporization of the high-boiling-point heat medium R1 (i.e., production of the high-boiling-point heat medium vapor R2) by the high-boiling-point heat medium vapor generator 2.

The high-boiling-point heat medium vapor R2 discharged from the high-boiling-point heat medium vapor generator 2 becomes the high-boiling-point heat medium vapor R2 (superheated high-boiling-point heat medium vapor) superheated beyond the boiling point by heat exchange with the high-temperature exhaust gas G in the high-boiling-point heat medium vapor super generator 6. The region of the exchanged heat amount points C1 to C2 in the broken line Lk is the superheated region of the high-boiling-point heat medium vapor R2 due to the high-boiling-point heat medium vapor superheater 6.

Here, the high-boiling-point heat medium R1 supplied to the high-boiling-point heat medium preheater 4 by the high-boiling-point heat medium supply pump 8 is liquefied in the high-boiling-point heat medium vapor condenser 11 by heat exchange between the high-boiling-point heat medium vapor R2 discharged from the high-boiling-point heat medium vapor turbine power generator 10 and the water R3 discharged from the water preheater 5. Heat exchange in the high-boiling-point heat medium vapor condenser 11 corresponds to the region of the exchanged heat amount points D to B1 in the broken line Lk.

In the region of the exchanged heat amount points D to B1 in the broken line Lk, the heat from heat exchange initially acts upon the high-boiling-point heat medium vapor R2 as sensible heat, with the result that the temperature of the high-boiling-point heat medium vapor R2 gradually declines, after which the heat acts upon the high-boiling-point heat medium vapor R2 as latent heat, with the result that the high-boiling-point heat medium vapor R2 is condensed in a constant quantity while temperature is maintained at a constant value. This change in condition of the high-boiling-point heat medium vapor R2 pertains to the case where the high-boiling-point heat medium R1 is ethylene glycol (molecular formula: C₂H₆O₂), and varies according to the type of the high-boiling-point heat medium R1.

Specifically, in the exhaust heat recovery unit K1 of the energy supply system P1, the water R3 of a condition Ys corresponding to the exchanged heat amount point A1 becomes the water vapor R4 of a condition Xs superheated to a temperature corresponding to the exchanged heat amount point C3 of the broken line Ls by heat exchange with the high-temperature exhaust gas G of comparatively low temperature in the water preheater 5 and the water vapor generator 3, heat exchange with the high-boiling-point heat medium vapor R2 (high-boiling-point heat medium vapor) in the high-boiling-point heat medium vapor condenser 11, and heat exchange with the high-temperature exhaust gas G of comparatively high temperature in the water vapor superheater 7. The water vapor R4 of the condition Xs is then supplied to the water vapor turbine power generator 13 as a source of dynamic force, and releases energy, after which it is cooled, condensed, restored to water, and returned to the water R3 of the condition Ys corresponding to the exchanged heat amount point A1.

Moreover, in the exhaust heat recovery unit K1, the high-boiling-point heat medium R1 of a condition Yk corresponding to the exchanged heat amount point D becomes the high-boiling-point heat medium vapor R2 of a condition Xk superheated to a temperature corresponding to the exchanged heat amount point C2 of the broken line Lk by heat exchange with the high-temperature exhaust gas G of comparatively high temperature in the high-boiling-point heat medium preheater 4, the high-boiling-point heat medium vapor generator 2, and the high-boiling-point heat medium vapor superheater 6. The high-boiling-point heat medium vapor R2 of the condition Xk is then supplied to the high-boiling-point heat medium vapor turbine power generator 10 as a source of dynamic force, and releases energy, thereby returning to the high-boiling-point heat medium R1 of a condition YL corresponding to the exchanged heat amount point D.

According to the exhaust heat recovery unit K1, in addition to conducting exhaust heat recovery by vaporizing the water R3 by heat exchange with the high-temperature exhaust gas G to convert it to the water vapor R4, exhaust heat recovery is also conducted by vaporizing the high-boiling-point heat medium R1 which has a higher evaporation temperature than the water R3 (i.e., a lower evaporation pressure than the water R3) by heat exchange with the high-temperature exhaust gas G to convert it to the high-boiling-point heat medium vapor R2, thereby enabling improvement in available energy recovery efficiency compared to conventional exhaust heat recovery methods.

Specifically, it is possible to constitute a Rankine cycle which extracts dynamic force by the enthalpy difference of the condition Xk (gas phase) and the condition YL (gas phase or mixed gas-liquid phase) by application of the high-boiling-point heat medium R1. With respect to a low-boiling-point heat medium (conventional freon or freon substitute) with a lower boiling point than the water R3, since the high-temperature zone exceeds the critical point, extraction of dynamic force by a Rankine cycle is not possible. That is, according to the exhaust heat recovery unit K1, use of the high-boiling-point heat medium R1 enables efficient extraction of available energy in the high-temperature zone, which is impossible with a low-boiling-point heat medium.

Moreover, according to the exhaust heat recovery unit K1, since the high-boiling-point heat medium vapor R2 is superheated using the high-boiling-point heat medium vapor superheater 6, and since the water vapor R4 is superheated using the water vapor superheater 7, heat recovery efficiency can be further improved compared to conventional exhaust heat recovery methods.

Second Embodiment

Next, a second embodiment of the present invention is described with reference to FIGS. 3 and 4.

In FIG. 3, components identical to components of the energy supply system P1 of the first embodiment shown in FIG. 1 are given the same reference symbols.

The energy supply system P2 of the second embodiment includes an exhaust heat recovery unit K2 and a power generation/vapor output unit W2. As shown in FIG. 3, the energy supply system P2 has a configuration which omits the water vapor superheater 7, the water vapor turbine power generator 13, the water vapor condenser 14, the water collection tank 15, and the cooling water supply device 16 from the energy supply system P1 of the first embodiment. That is, in the energy supply system P2, the water vapor R4 discharged from the water vapor generator 3 and the water vapor R4 discharged from the high-boiling-point heat medium vapor condenser 11 are merged, and supplied to an external water vapor load, and restored water recovered from the water vapor load is input to the water supply pump 9.

In the energy supply system P2, as shown in FIG. 3, the exhaust heat recovery unit K2 omits the water vapor superheater 7, and is configured from the exhaust gas pipe 1, the high-boiling-point heat medium vapor generator 2, the water vapor generator 3, the high-boiling-point heat medium preheater 4, the water preheater 5, and the high-boiling-point heat medium vapor superheater 6. The power generation/vapor output unit W2 is configured from the high-boiling-point heat medium supply pump 8, the water supply pump 9, the high-boiling-point heat medium vapor turbine power generator 10, the high-boiling-point heat medium vapor condenser 11, and the liquid collection tank 12.

The heat exchange conditions of the respective heat mediums (i.e., the high-temperature exhaust gas G, the high-boiling-point heat medium R1, the high-boiling-point heat medium vapor R2, the water R3, and the water vapor R4) in the heat exchange region of the exhaust heat recovery unit K2 are shown in FIG. 4. Specifically, when considering heat exchange of the water R3 and the water vapor R4 with the high-temperature exhaust gas G, i.e., heat exchange in the water preheater 5 and the water vapor generator 3, as shown in a broken line Ls1, the water R3 of a condition Ys1 corresponding to an exchanged heat amount point Aa is preheated to an exchanged heat amount point Ab which is a temperature slightly below the boiling point by heat exchange with the high-temperature exhaust gas G of comparatively low temperature in the water preheater 5, and then becomes the water vapor R4 of a condition Xs1 corresponding to an exchanged heat amount point Da by heat exchange with the high-temperature exhaust gas G in the water vapor generator 3 and by heat exchange with the high-boiling-point heat medium vapor R2 (high-boiling-point heat medium vapor) in the high-boiling-point heat medium vapor condenser 11. The water vapor R4 of the condition Xs1 is supplied as a heat source to the external heat load, and releases energy in the external heat load, thereby returning to the water R3 of the condition Ys1 corresponding to the exchanged heat amount point Aa.

On the other hand, the high-boiling-point heat medium R1 of a condition Yk1 corresponding to an exchanged heat amount point B1 becomes the high-boiling-point heat medium vapor R2 of a condition corresponding to an exchanged heat amount point C1 of a broken line Lk1 by heat exchange with the high-temperature exhaust gas G of comparatively high temperature in the high-boiling-point heat medium preheater 4 and the high-boiling-point heat medium vapor generator 2, and the high-boiling-point heat medium vapor R2 becomes the high-boiling-point heat medium vapor R2 (superheated high-boiling-point heat medium vapor) of a condition Xk1 superheated beyond the boiling point by heat exchange with the high-temperature exhaust gas G in the high-boiling-point heat medium vapor superheater 6. The high-boiling-point heat medium vapor R2 (superheated high-boiling-point heat medium vapor) of the condition Xk1 is then supplied to the high-boiling-point heat medium vapor turbine power generator 10 as dynamic drive force, and releases energy, thereby returning to the high-boiling-point heat medium R1 of a condition YL1 corresponding to the exchanged heat amount point Da.

Specifically, the energy supply system P2 is a cogeneration system which supplies electrical energy to the exterior, and which also supplies thermal energy to the exterior by water vapor. According to the exhaust heat recovery unit K2 of the energy supply system P2, as with the exhaust heat recovery unit K1 of the energy supply system P1 of the first embodiment, in addition to exhaust heat recovery which produces the water vapor R4 from the water R3 by heat exchange with the high-temperature exhaust gas G, exhaust heat recovery is also conducted which produces the high-boiling-point heat medium vapor R2 from the high-boiling-point heat medium R1 which has a higher evaporation temperature than the water R3 (i.e., a lower evaporation pressure than the water R3) by heat exchange with the high-temperature exhaust gas G, thereby enabling improvement in available energy recovery efficiency compared to conventional heat recovery methods.

Here, when total efficiency is calculated in the case where ethylene glycol (molecular formula: C₂H₆O₂) is adopted and in the case where diethylene glycol (molecular formula: C₂H₁₀O₃) is adopted as the high-boiling-point heat medium R1, it is 81.26% (=30.56% (power generation efficiency)+50.70% (exhaust heat recovery efficiency)) in the case of ethylene glycol, and 80.66% (=33.15% (power generation efficiency)+47.56% (exhaust heat recovery efficiency)) in the case of diethylene glycol.

Specifically, total efficiency is slightly higher when ethylene glycol is used than when diethylene glycol is used, but power generation efficiency is higher when diethylene glycol is used than when ethylene glycol is used. This difference in power generation efficiency derives from the gas-liquid pressure differential of the two heat mediums. Under identical temperature conditions, in the case where the gaseous pressure of the two heat mediums is, for example, 1.5 MPa, the liquid pressure of ethylene glycol is 0.109 MPa, while the liquid pressure of diethylene glycol is 0.027 MPa. In short, since diethylene glycol has a lower liquid pressure than ethylene glycol, diethylene glycol has a larger gas-liquid pressure differential than ethylene glycol. This difference in gas-liquid pressure differential is the cause of power generation efficiency.

FIG. 5 shows the energy-saving rate when ethylene glycol is used as the high-boiling-point heat medium R1, and when diethylene glycol is used for that purpose. FIG. 5 shows an energy-saving rate of η_(s1) when ethylene glycol is used and an energy-saving rate of η_(s2) when diethylene glycol is used, in a characteristic diagram which renders gross thermal efficiency of power generation η_(E) under a low heat value (LHV) standard on the horizontal axis and exhaust heat recovery efficiency η_(H) on the vertical axis. As shown in FIG. 5, the energy-saving rate η_(s1) is 23.5%, while the energy-saving rate ƒ_(s2) is 25.1%, indicating that a slightly higher value is obtained when diethylene glycol is used than when ethylene glycol is used.

Furthermore, FIG. 6 shows the CO₂ reduction rate when ethylene glycol is used as the high-boiling-point heat medium R1, and when diethylene glycol is used for that purpose. FIG. 6 shows a CO₂ reduction rate of S₁ when ethylene glycol is used and a CO₂ reduction rate of S₂ when diethylene glycol is used, in a characteristic diagram which renders gross thermal efficiency of power generation η_(E) under a low heat value (LHV) standard on the horizontal axis and exhaust heat recovery efficiency η_(H) on the vertical axis. As shown in FIG. 6, the CO₂ reduction rate S₁ is 38.4%, while the CO₂ reduction rate S₂ is 40.4%, indicating that a slightly higher value is obtained when diethylene glycol is used than when ethylene glycol is used, as with the aforementioned energy-saving rate.

The energy supply system P2 is a cogeneration system which supplies electrical energy to the exterior, and which also supplies thermal energy to the exterior by water vapor. The energy supply system P2 differs from an energy supply apparatus which converts available energy obtained by exhaust heat recovery from exhaust gas only to electrical energy for supply to the exterior, as with the energy supply system P1 of the first embodiment, or from an energy supply apparatus which converts available energy only to thermal energy for supply to the exterior, as with well-known exhaust heat recovery boilers. With these energy supply apparatuses, as available energy is converted to a single type of energy such as electrical energy or thermal energy, it is not possible to achieve high energy saving rates and CO₂ reduction rates as with the energy supply system P2.

Third Embodiment

Next, a third embodiment of the present invention is described with reference to FIGS. 7 and 8. In FIG. 7, components identical to components of the energy supply system P2 of the second embodiment shown in FIG. 3 are given the same reference symbols.

As shown in FIG. 7, the principal feature of an energy supply system P3 of the third embodiment is that it replaces the water vapor generator 3 with a flash tank 17 in the energy supply system P2 of the second embodiment. The energy supply system P3 is further provided with a pressurizing pump 18 as an ancillary component of the flash tank 17.

Specifically, an exhaust heat recovery unit K3 in the energy supply system P3 includes the exhaust gas pipe 1, the high-boiling-point heat medium vapor generator 2, the high-boiling-point heat medium preheater 4, the water preheater 5, the high-boiling-point heat medium vapor superheater 6, and the flash tank 17. In addition, a power generation/vapor output unit W3 includes the high-boiling-point heat medium supply pump 8, the water supply pump 9, the high-boiling-point heat medium vapor turbine power generator 10, the high-boiling-point heat medium vapor condenser 11, the liquid collection tank 12, and the pressurizing pump 18.

The flash tank 17 is a flash type water vapor generator which converts water (high-temperature high-pressure water) supplied from the water preheater 5 to water vapor by the flash phenomenon. The flash tank 17 is a type of container in which internal pressure is adjusted so that the water (high-temperature high-pressure water) supplied from the water preheater 5 is vaporized by the flash phenomenon and produces the water vapor R4 (flash vapor) and saturated water R5. The flash phenomenon is known as a phenomenon where a portion of high-temperature high-pressure water is vaporized as saturated water vapor when the high-temperature high-pressure water is discharged to a space with a low-pressure atmosphere to release pressure.

The pressurizing pump 18 is a pump which pressurizes water collected from an external heat load. The water discharged from the pressurizing pump 18 is distributed and supplied to the water supply pump 9 and the high-boiling-point heat medium vapor condenser 11. The water vapor R4 generated in the flash tank 17 is supplied to the external heat load, and the saturated water R5 similarly generated in the flash tank 17 is distributed and supplied to the water supply pump 9 and the high-boiling-point heat medium vapor condenser 11 by, for example, supplying it to a bifurcation point j of the water supply pump 9 and the high-boiling-point heat medium vapor condenser 11 for the water discharged from the pressurizing pump 18, as illustrated in the drawing.

Specifically, instead of the water vapor generator 3 of the second embodiment which generates the water vapor R4 by the action of heat obtained by heat exchange between the water R3 and the high-temperature exhaust gas G, the energy supply system P3 is provided with the flash tank 17 which generates the water vapor R4 by the action of pressure (reduced pressure).

Since the pressure of the water collected from the external heat load is lower than the pressure of the saturated water R5 output from the flash tank 17, if the pressurizing pump 18 were not provided, it would be difficult to supply water at sufficient pressure to the high-boiling-point heat medium vapor condenser 11, and the supply efficiency of the water vapor R4 to the exterior would decline. Accordingly, although not an indispensable component of the third embodiment, provision of the pressurizing pump 18 is preferable.

FIG. 8 shows the heat exchange conditions of the respective heat mediums (i.e., the high-temperature exhaust gas G, the high-boiling-point heat medium R1, the high-boiling-point heat medium vapor R2, the water R3, and the water vapor R4) in the exhaust heat recovery unit K3 of the energy supply system P3. As shown by a broken line Ls2 of FIG. 8, it is possible to preheat the water R3 in a region extending across exchanged heat amount points Aa to B1, i.e., in a wider region than the region extending across the exchanged heat amount points Aa to Ab of the second embodiment.

Due to heat exchange between the water R3 and the high-temperature exhaust gas G in the region extending across the exchanged heat amount points Aa to B1, it is possible to obtain a greater amount of available energy from the high-temperature exhaust gas G, as is clear from a comparison with FIG. 4 which shows the heat exchange conditions of the second embodiment. Therefore, according to the third embodiment, since a greater amount of the water R3 can be preheated, it is possible to generate a greater amount of the water vapor R4 than in the second embodiment. According to the third embodiment, it is possible to reduce the cost of the system, because the flash tank 17 is used instead of the water vapor generator 3.

The present invention is not limited to the respective foregoing embodiments, and the following variations are, for example, conceivable.

(1) In the respective foregoing embodiments, heat is recovered from the exhaust heat of the high-temperature exhaust gas G using two types of liquid with different vapor pressures, i.e., in addition to the water R3, the high-boiling-point heat medium R1 which has a lower vapor pressure than the water R3. Alternatively, it is also acceptable to conduct heat recovery from the exhaust heat of the high-temperature exhaust gas G using only the high-boiling-point heat medium R1, or three or more types of liquid having different vapor pressures.

For example, in the case where heat recovery is conducted from the exhaust heat of the high-temperature exhaust gas G using only the high-boiling-point heat medium R1, although depending on the temperature of the high-temperature exhaust gas G, heat exchange is possible with a smaller temperature difference than when using the water R3, thereby enabling improvement in available energy recovery efficiency compared to the conventional case where only the water R3 is used. In addition to the high-boiling-point heat medium R1 and the water R3, it is also acceptable to conduct heat recovery from the exhaust heat of the high-temperature exhaust gas G with the additional combination of a low-boiling-point heat medium that has a lower boiling point than the water R3.

(2) In the first and second embodiments, the high-boiling-point heat medium preheater 4 and the water preheater 5 are used as components, but it is also acceptable to omit the high-boiling-point heat medium preheater 4 and the water preheater 5 as necessary, although heat recovery efficiency will decline.

(3) Each of the foregoing embodiments relate to the case where heat is recovered from the exhaust heat of the high-temperature exhaust gas G, but the heat source (exhaust heat) that is the object of heat recovery is not limited to the high-temperature exhaust gas G (gas). For example, it may also be a liquid or solid with a high temperature exceeding 300° C. Accordingly, the thermal conduction path in the present invention is not limited to the exhaust gas pipe 1 through which the high-temperature exhaust gas G (gas) flows.

(4) Each of the foregoing embodiments use the high-boiling-point heat medium vapor turbine power generator 10 and the water vapor turbine power generator 13 as components in order to generate power which is one mode of dynamic force. Alternatively, various modes of dynamic force may also be extracted by connection to compressors, wind turbines, pumps, propellers and the like as driven equipment.

(5) The third embodiment replaces the water vapor generator 3 of the second embodiment with the flash tank 17, but it is also conceivable to replace the water vapor generator 3 of the first embodiment with the flash tank 17.

(6) In the third embodiment, one flash tank 17 is provided, but it is also acceptable to provide a plurality of flash tanks 17 in alignment, and convert the water R3 output from the water preheater 5 to water vapor by the plurality of aligned flash tanks 17.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide an exhaust heat recovery system and an exhaust heat recovery method with a higher available energy recovery efficiency than an exhaust heat recovery method which obtains available energy by vaporizing water, or than an exhaust heat recovery method which obtains available energy by vaporizing water and a liquid with a lower boiling point than the water.

Moreover, according to the present invention, it is possible to provide an energy supply system with higher energy efficiency than conventional systems, because of the higher available energy recovery efficiency in exhaust heat recovery as described above.

REFERENCE SIGNS LIST

-   1: exhaust gas pipe (thermal conduction path) -   2: high-boiling-point heat medium vapor generator -   3: water vapor generator -   4: high-boiling-point heat medium preheater -   5: water preheater -   6: high-boiling-point heat medium vapor superheater -   7: water vapor superheater -   8: high-boiling point heat medium supply pump -   9: water supply pump -   10: high-boiling-point heat medium vapor turbine power generator -   11: high-boiling-point heat medium vapor condenser (heat exchanger) -   12: liquid collection tank -   13: water vapor turbine power generator -   14: water vapor condenser -   15: water collection tank -   16: cooling water supply device -   17: flash tank -   18: pressurizing pump -   G: high-temperature exhaust gas -   R1: high-boiling-point heat medium -   R2: high-boiling-point eat medium vapor -   R3: water -   R4: water vapor -   P1 to P3: energy supply system -   K1 to K3: exhaust heat recovery unit (exhaust heat recovery system) -   W1: power generation unit -   W2, W3: power generation/vapor output unit 

1. An exhaust recovery system, comprising: a thermal conduction path which conducts exhaust heat; and a high-boiling-point heat medium vapor generator which generates high-boiling-point heat medium vapor by heat exchange between a high-boiling-point heat medium that has a higher evaporation temperature than water and the exhaust heat conducted through the thermal conduction path.
 2. The exhaust heat recovery system according to claim 1, further comprising a water vapor generator which is provided in the thermal conduction path on the downstream side of the high-boiling-point heat medium vapor generator, and which generates water vapor by heat exchange between the water and the exhaust heat.
 3. The exhaust heat recovery system according to claim 1, further comprising, on the upstream side of the high-boiling-point heat medium vapor generator in the thermal conduction path, either one or both of a high-boiling-point heat medium vapor superheater which superheats the high-boiling-point heat medium vapor by heat exchange with the exhaust heat, or a water vapor superheater which superheats the water vapor by heat exchange with the exhaust heat.
 4. The exhaust heat recovery system according to claim 1, further comprising a high-boiling-point heat medium preheater which preheats the high-boiling-point heat medium and/or a water preheater which preheats the water.
 5. The exhaust heat recovery system according to claim 1, wherein the thermal conduction path is an exhaust gas pipe through which exhaust gas possessing the exhaust heat flows.
 6. The exhaust heat recovery system according to claim 1, wherein the high-boiling-point heat medium is ethylene glycol, diethylene glycol, propylene glycol, propylene ethylene glycol, or formamide.
 7. The exhaust heat recovery system according to claim 4, wherein, instead of the water vapor generator, a flash type water vapor generator which converts the water preheated in the water preheater to the water vapor by the flash phenomenon is provided.
 8. An energy supply system, comprising: the exhaust heat recovery system according to claim 1; and a dynamic force generation unit which supplies the high-boiling-point heat medium and/or the water to the exhaust heat recovery system, recovers the high-boiling-point heat medium vapor and/or the water vapor from the exhaust heat recovery system, and generates dynamic force using the high-boiling-point heat medium vapor and/or the water vapor as working fluid.
 9. The energy supply system according to claim 8, wherein the dynamic force generation unit includes a heat exchanger which carries out heat exchange between the water and the high-boiling-point heat medium vapor after being provided for generation of the dynamic force to condense and liquefy the high-boiling-point heat medium vapor, and to generate the water vapor.
 10. An exhaust heat recovery method, which performs heat recovery by vaporizing a high-boiling-point heat medium having a higher evaporation temperature than water by exhaust heat.
 11. The exhaust heat recovery method according to claim 10, wherein heat recovery is performed by vaporizing water by the exhaust heat after heat recovery using the high-boiling-point heat medium.
 12. The exhaust heat recovery method according to claim 10, wherein high-boiling-point heat medium vapor and/or water vapor are superheated by heat exchange with the exhaust heat.
 13. The exhaust heat recovery method according to claim 10, wherein the high-boiling-point heat medium is ethylene glycol, diethylene glycol, propylene glycol, propylene ethylene glycol, or formamide.
 14. The exhaust heat recovery method according to claim 11, wherein, instead of performing heat recovery by vaporizing the water by the exhaust heat after heat recovery using the high-boiling-point heat medium, heat recovery is preformed by preheating the water by the exhaust heat after heat recovery using the high-boiling-point heat medium, and then vaporizing the preheated water by the flash phenomenon. 